The area has been scene of occasional clashes between Iranian forces and militant groups believed to be affiliated with al-Qaida.

Four of the guards killed in the attack in the restive Sistan-Baluchistan province on Monday were conscripts, said Fars. It also said three of the attackers were killed in the shootout with the militants.

It was the second reported incident on Monday in Sistan-Baluchistan near the Pakistani border. Earlier, Iran's official IRNA news said Revolutionary Guard units broke up a militant group linked to a "foreign intelligence" agency, killed three of its members and detained several. IRNA also said Guard forces confiscated a large amount of weapons and communication equipment from the militant group.

Fars said a militant group known as Jeish al-Adl — meaning Army of Justice in English — on Tuesday claimed responsibility for the attack on its Twitter page. It said the group's members targeted border guards in the town of Negur on Monday night, after crossing over from Pakistan.

There was no immediate comment from Pakistani officials on the incident.

Jeish al-Adl has been behind several attacks in Iran over the past two years and is believed affiliated with al-Qaida. In January, Iran reported arresting 20 members of the group in Sistan-Baluchistan.